Three genuinely different problems that get treated as one. Here is how to tell them apart before you spend money on the wrong fix.
If you have a damp patch on a wall, the honest first question is not "who do I call" but "what actually is this." Rising damp, penetrating damp and condensation are three different mechanisms with three different fixes, and treating the wrong one wastes money and leaves the real problem untouched.
Rising damp is groundwater travelling up through the capillaries in brickwork or mortar, usually because the damp proof course has failed or was never installed. It produces a fairly even tide mark low down on the wall, typically no higher than a metre or so, along with decaying skirting boards, bubbling plaster and, in older buildings, a build-up of ground salts that keep drawing moisture back in even after a wall is dried out.
It is worth saying plainly: genuine rising damp is rarer than the industry that treats it would have you believe. In an occupied, heated home, most damp reported as "rising" turns out on proper diagnosis to be condensation instead.
Penetrating damp is water getting in through a defect in the building itself, a cracked render, a failed pointing joint, a leaking gutter, a gap around a window reveal. Unlike rising damp it can appear at any height, and it is usually traceable to one specific point of entry rather than spread evenly along a wall. A damp patch under a chimney breast after heavy rain, or a stain that only appears near a particular window, points to penetrating damp rather than rising damp or condensation.
Condensation happens when warm, moisture-laden air inside the home meets a cold surface, a window, an external wall, the corner of a room with poor airflow, and the water vapour turns back into liquid water on contact. It is a ventilation and heating problem, not a structural one, and it is by far the most common of the three, especially in winter, in bathrooms and bedrooms, and in older solid-wall properties where external walls run colder than a modern cavity wall.
You do not need a £300 survey to get a first read on which of the three you are dealing with. Tape a sheet of kitchen foil to the affected wall, sealing all four edges tightly so no room air can get behind it, and leave it for 24 to 48 hours.
Chemical damp proof courses and injection treatments are built to stop moisture rising through masonry. They do nothing for condensation, because condensation is not coming from inside the wall at all, it is water vapour from cooking, showering, breathing and drying laundry, meeting a cold surface. If your actual problem is condensation and you pay for a rising-damp treatment, the black mould will be back within a season because the real cause, warm air meeting a cold wall with nowhere for the moisture to go, was never addressed.
That is the specific problem a whole-house dehumidifier and fresh air system is built to solve: it treats the humidity and ventilation of the whole property continuously, rather than chasing individual damp patches room by room.
Book a free, no-obligation survey and we'll tell you honestly what's causing it, not just sell you a fix.
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